1. Field of the Invention
The present invention relates to gas leakage detection and fail-safe control method for a gas-fueled internal. combustion engine, and more particularly to a gas leakage detection and fail-safe control method that can detect even small amounts of gas leakage and that, when gas leakage is detected, controls a gas shut-off valve for fail-safe purposes and issues a warning. The invention also relates to an apparatus for implementing such a method.
2. Description of the Related Art
Gas fuels, such as natural gas, have been used as automobile fuels in recent years. In use, natural gas is filled under pressure into a container; to supply this pressure-filled compressed natural gas (CNG) into an engine, an injector valve is used, as in the case of gasoline.
A vehicle injector device is designed to pass an electric current through the magnetic coil of the injector under electronic control, and the resulting magnetic force moves an injector valve, thereby forming a gap between it and an injection nozzle and thus allowing the fuel to flow through the gap.
A gas-fueled internal combustion engine uses, instead of gasoline, compressed natural gas as a fuel as described above and, since high-pressure natural gas is stored in the tank, a sensor for detecting gas pressure is mounted to detect gas leakage. When gas leakage occurs, a fail-safe operation is performed which involves, for example, closing the gas shut/off valve.
However, the reality is that, since the gas leakage detection is performed with the gas shut-off valve open when the engine is running, for example, when the vehicle is moving, it is difficult to detect a small amount of gas leakage when the gas pressure is high. That is, it is difficult to distinguish whether a gas pressure decrease is the result of gas consumption by the engine or is caused by gas leakage.
It is, accordingly, an object of the present invention to provide a method and apparatus that can detect even small amounts of gas leakage and, when gas leakage is detected, can perform a proper fail-safe operation.
To attain the above object, the gas leakage detection and fail-safe control method for a gas-fueled internal combustion engine according to the present invention calculates the amount of decrease of gas pressure when the engine is stopped and the gas shut-off valve is closed, by comparing initial gas pressure with the gas pressure detected after the elapse of a prescribed time, and detects gas leakage by determining that gas is leaking if the amount of decrease is larger than a predetermined value. In one embodiment, each time the engine is stopped, the accumulated value of the amount of decrease of gas pressure is calculated, and gas leakage is detected by determining that gas is leaking if the accumulated value is larger than a predetermined value.
In another embodiment, the rate of decrease of gas pressure from the initial gas pressure to the gas pressure detected after the elapse of a prescribed time is calculated, and gas leakage is detected by determining that gas is leaking if the rate of decrease is larger than a predetermined value. In a further embodiment, each time the engine is stopped, the accumulated value of the rate of decrease of gas pressure is calculated, and gas leakage is detected by determining that gas is leaking if the accumulated value is larger than a predetermined value.
When gas leakage is detected, a fail-safe operation is performed, for example, by closing a delivery gas shut-off valve and issuing a warning.